Commercially cultivated jute is mainly produced from two species, namely, Corchorus olitorius (commonly called “tossa jute”) and Corchorus capsularis (commonly called “white jute”). Both species are diploid (2n=14), and only two of which are used in agriculture. These two species constitute an important cash crop for the South East Asian countries and for Brazil, providing biodegradable ligno-cellulose fiber. Fibers are commonly used as packaging materials for industrial products, and for production of other value-added products, such as yarns and textiles, ropes, twines and nets, non-woven fabrics, tissues, pulp and paper, geotextiles, composites and home textiles. Due to the environment-friendly and biodegradable characteristics of jute fiber, demand is increasing in the world market. In order to keep up with rising global demand, further improvement of jute fiber production is necessary. Jute fibers obtained from the bark of the stem and fibers are grouped into bundles. Fibers arranged as triangular wedges of sclerenchymatous fiber cells alternate with medullary rays of other soft tissue. These fiber cells differentiate from phloem and develop in four chronological stages—initiation, elongation, secondary cell wall thickening, and maturation stages. Little is known about the genetic control of jute fiber initiation and elongation. However, fiber length and uniformity are common requirements for most industrial uses. For example, long fiber and uniform cell are ideal for the production of fine fabrics for the textile industry. In the pulp industry, strength characteristics of pulp are determined in part by fiber length, pulp yield and alkali consumption, due to their strength and bonding properties. In order to meet industrial needs, the development of jute varieties with desirable fiber length as well as strength is necessary. Therefore, the biosynthesis of fiber and the molecular biology involved in fiber biosynthesis are of significant importance.
Bast fiber primarily begins from the apical meristem and, gradually, the fiber elongates, mostly through intrusive growth, until the onset of secondary wall development. Fiber cell elongation is a process which results from the interaction between internal turgor pressure and the mechanical strength of the cell wall, which is controlled endogenously. However, the mechanism and genes involved in fiber cell elongation have not been totally determined. Several candidate genes associated with the elongation and formation of cotton fibers have been identified. For example, five genes from cotton plants which are specially expressed at the cotton fiber elongation stage were identified by differential screening and display methods [U.S. Pat. Nos. 5,880,100 and 5,932,713, 6,225,536 and 6,166,294; all of which are incorporated by reference], but there is no such report in area of the jute and/or bast fiber initiation and elongation.
Homeobox-leucine zipper (HD-Zip) proteins are transcription factors unique to plants which are encoded by multiple copies of the genes in a plant genome. For example, Arabidopsis thaliana genome has more than 25 genes of this family. Among the genes, homeobox-leucine zipper protein HAT22 (HD-ZIP protein 22) is involved in the elongation of the vascular fiber cell.
HD-ZIP protein 22 is expressed in the interfascicular regions in which fibers differentiate, which is consistent with its role in the control of interfascicular fiber differentiation. Furthermore, it is also expressed in phloem during phases of secondary growth (Tornero et al. 1996), indicating its possible role in the regulation of vascular tissue formation (Zhong and Ye, 1999). Unlike other plant homeobox genes, HD-ZIP protein 22 is not expressed in meristems, and the function of HD-ZIP protein 22 is likely to participate in the regulation of the identity and/or activity of phloem tissues during secondary phases of vascular development (Tornero et al. 1996).
In view of the fact that Homeobox-leucine zipper protein HAT22 may play an important role in the spatial control of phloem fiber differentiation, it is desirable to take a genetic approach to understanding the biosynthesis of fiber in the plant by exploring and utilizing molecular biological and genetic information regarding homeobox-leucine zipper protein HAT22. Besides, because the fiber biosynthesis pathway and genetic make-up of each species of plant typically varies, a species-specific approach is also preferable in order to optimize yield of fiber from jute plants, and obtain compatible results to enable use in industry.